The present invention relates to an optical data recording/reproducing device.
An optical data recording/reproducing device is generally provided with an illuminating optical system and a monitoring optical system. The illuminating optical system includes a laser diode for emitting a laser beam and an objective optical system which converges the laser beam emitted by the laser diode on a recording medium such as an optical disc. Further, a beam splitter is provided to split the laser beam emitted by the laser diode such that a part of the beam is directed to the objective optical system, and another part of the laser beam is directed to the monitoring optical system. The monitoring optical system is provided with a light receiving element for receiving the laser beam split by the beam splitter to detect intensity of the laser beam emitted by the laser diode. Based on the output of the light receiving element, a driving circuit of the laser diode controls the intensity of the laser beam emitted by the laser diode. Thus the intensity of the laser beam emitted by the laser diode is automatically adjusted.
The amount of light emerged from the objective lens is proportional to the amount of light received by the light receiving element. However, beam radiation angles of individual laser diodes may be different from each other. Accordingly, a relationship between an amount of light emerged from the objective lens and an amount of light incident on the light receiving element may be different among respective optical data recording/reproducing devices. Therefore, the driving circuit should be constituted to deal with any possible proportional relationship between the amount of light emerged from the objective lens and an amount of light incident on the light receiving element
However, if a proportional coefficiency becomes too large, the driving circuit may not drive the laser diode, due to its limited dynamic range.
It may be possible to broaden the dynamic range of the driving circuit by modifying an electrical circuit thereof. However, the range which can be broadened by modifying the circuit is limited, and accordingly such a solution cannot be essential. Further, in order to broaden the dynamic range of the driving circuit, the circuit becomes complicated, which increases a manufacturing cost thereof.
Alternatively, only the laser diodes whose characteristics meet the dynamic range of the driving circuit are selected and used when the data recording/reproducing devices are assembled. However, if the step of selecting laser diodes is incorporated in the assembling procedure, the assembling procedure may take time and increases the manufacturing cost.
It is therefore an object of the invention to provide an optical data recording/reproducing device which is capable of compensating the individual differences of the characteristics of laser diodes, simplifying driving circuits, and adjusting the intensity of the laser beam emitted by the laser diode with suppressing increase of the manufacturing cost.
For the above object, according to the present invention, there is provided an optical data recording/reproducing device, which is provided with a laser diode for emitting laser beam, an illuminating optical system including an objective lens which converges the laser beam emitted by the laser diode on an optical disc, a monitoring optical system including a light receiving element which receives a part of the laser beam emitted by the laser diode, and a driving circuit which drives the laser diode in accordance with an output signal of the light receiving element. It should be noted that a first coupling efficiency of the illuminating optical system and a second coupling efficiency of the monitoring optical system are made substantially the same.
With this constitution, the amount of light emerged from the objective lens is proportional to the amount of light received by the light receiving element. Therefore, the driving circuit can be made simple since characteristics of the laser diode does not affect driving of the laser diode.
Optionally, the device may be provided with a beam splitter which divides the laser beam emitted by the laser diode into a first beam directed to the illuminating optical system and a second beam directed to the monitoring optical system.
The beam splitter may has a reflection surface which reflects a part of light incident thereon, and allows the other to pass through. The reflection ratio of the reflection surface define a proportional coefficiency between the amount of light emerged from the objective lens and the amount of light received by the light receiving element.
It should be noted that the first coupling efficiency is defined as a ratio of an amount of light emerged from the objective lens to an amount of light entering the illuminating optical system, and the second coupling efficiency is defined as a ratio of an amount of light received by the light receiving element to an amount of light entering the monitoring optical system.
In particular, the illuminating optical system may include an aperture which regulates amount of light incident on the objective lens, the aperture defining the first coupling efficiency.
In this case, the monitoring optical system may include a second aperture which regulates amount of light incident on the light receiving element, the second aperture defining the second coupling efficiency.
Optionally, the monitoring optical system may include a converging lens between the second aperture and the light receiving element, light passed through the second aperture being converged by the converging lens.
Alternatively, the light receiving element has a light receiving area which is configured to receive a part of the second light so as to regulate amount of light received by the light receiving element, a size of the light receiving area defining the second coupling efficiency.
Still alternatively, the monitoring optical system may include an imaging lens mounted on a body member, the light receiving element being accommodated in the body member, and only a part of the second light incident on the imaging lens passing through the imaging lens and directed to the light receiving element, diameter of the imaging lens defining the second coupling efficiency.
Optionally, the imaging lens may have a hemispherical shape.
According to another aspect of the invention, there is provided an optical data recording/reproducing device, which is provided with, a laser diode for emitting laser beam, an illuminating optical system including an objective lens which converges the laser beam emitted by the laser diode on an optical disc. A monitoring optical system may include a light receiving element which receives a part of the laser beam emitted by the laser diode, and a first coupling efficiency of the illuminating optical system and a second coupling efficiency of the monitoring optical system are made substantially the same.
Optionally, the device may include a beam splitter which divides the laser beam emitted by the laser diode into a beam directed to the illuminating optical system and a beam directed to the monitoring optical system.
According to further aspect of the invention, there is provided an optical data recording/reproducing device, which is provided with a laser diode for emitting laser beam, an illuminating optical system including an objective lens which converges the laser beam emitted by the laser diode on an optical disc, and a monitoring optical system including a light receiving element which receives a part of the laser beam emitted by the laser diode. The device is constituted such that amount of light emerged from the objective lens is proportional to the amount of light received by the light receiving element regardless of characteristics of the laser diode.